Down-the-hole drill hammer

ABSTRACT

The present invention relates to an arrangement pertaining to down-the-hole hammers in which a driver ( 7 ) is adapted to transfer torsion forces between a rotating outer tube ( 10 ) and a drill bit ( 1 ) of the hammer, wherein the outer tube ( 10 ) surrounds all of the driver ( 7 ).

The present invention relates to an arrangement pertaining to down-the-hole hammers.

In the case of down-the-hole hammers, rotational forces, feed, and percussion energy are transferred from a drilling unit to a down-the-hole hammer, which is lowered into the hole to be drilled. The rotational forces are transmitted with the aid of a rotating outer tube, causing the drill bit to rotate, and the percussion forces are transmitted with the aid of a piston or ram that moves reciprocatingly in the tube in its longitudinal direction. The rotational force is transferred from the outer tube by means of a chuck or driver screwed firmly into the outer tube. Arranged inside the driver or chuck is an array of splines which co-act with splines arranged on the outside of the bit shaft. The driver/chuck is thus seated in the connection between the drill bit and the outer tube and the end of the driver/chuck facing towards the head of the drill bit has an outer diameter that corresponds roughly to the outer diameter of the outer tube and forms a direct extension thereof. The drilling bit, the outer tube and the driver or chuck are all made of steel.

In an attempt to solve problems arising from the formation of cracks or fissures that can cause the shaft of the bit to break at the spline connection to the driver, it has been proposed to replace the steel in the driver with a softer material, for instance with a bronze alloy. Unfortunately, this replacement has resulted in external wear and tear on the driver due to the backflow of cuttings along the outer surfaces of the drill bit, the driver and the outer tube. Although such wear can be observed from without and a change to a new driver can be made when it is seen that said element has worn down to an extent that makes such a change necessary, the new driver will normally have a larger diameter than the worn outer tube, therewith resulting in greater turbulence around the new driver and accelerated wear on the outer tube.

Accordingly, an object of the invention is to provide a novel arrangement that enables these problems to be avoided.

This object is achieved with an arrangement pertaining to down-the-hole hammers in which a driver is adapted to transmit torsion forces between a rotating outer tube and a drill bit belonging to the down-the-hole hammer, wherein the outer tube is arranged to fully surround the outside of the driver, in accordance with the invention.

Total enclosure of the driver by the outer tube enables the driver to be made of a softer material without being subjected to external abrasion that would result in premature wear on the driver. Such external wear would only affect the outer tube, the material of which is considerably harder and much more wear resistant than that from which the driver is made. Moreover, the outer tube can be given a surface coating which will make abrasive wear on the outer tube lower nevertheless.

The invention will now be described in more detail with reference to an exemplifying embodiment and also with reference to the accompanying drawings, in which FIG. 1 is a longitudinally sectioned view of a drill bit for a down-the-hole hammer and shows those parts that are in closest connection with the drill bit in accordance with known technology; and FIG. 2 is a corresponding longitudinally sectioned view of a drill bit for a down-the-hole hammer, showing those parts that are in closest connection with the drill bit in accordance with the present invention.

FIG. 1 thus shows a drill bit 1 that has rock drilling buttons 2 mounted on its front end in a known manner. Typically, the drill bit 1 also includes a shaft 3 which is provided with longitudinally extending splines 4 along a part of its length. The drill bit also has a rear end 5 against which a percussion piston is intended to strike. The drill bit 1 typically includes a longitudinally extending channel 6 through which compressed air is blown out from the front part of the drill to blow the drill cuttings away from the bit and out of the drill hole.

The shaft 3 carries a driver 7 which is provided internally with longitudinally extending splines 8 that co-act with the splines 4. The driver 7 is generally in the form of a sleeve and is provided along at least part of its length with an external screw thread 9 by means of which the driver 7 can be screwed securely to the front end of an outer tube 10 that surrounds at least a part of both the driver 7 and the shaft 3 of the drill bit 1. The outer tube 10 also surrounds the percussion piston 11. The drill hammer can be spliced or joined to allow the drill run to be extended to a desired length. The drilling unit causes the outer tube 10 to rotate, wherewith the rotational movement of the tube is transmitted to the driver 7 which, in turn, transfers the rotational movement to the drill bit 1 through the medium of the spline connection 8, 4.

As will be seen from FIG. 1, the end part 12 of the driver 7 facing towards the head 13 of the drill bit 1 has an outer diameter which corresponds essentially to the outer diameter of the outer tube 10 and constitutes an extension thereof. Thus, it is this end part 12 of the driver 7 and the outer tube 10 that are strongly abraded by the externally flowing cuttings.

FIG. 2 illustrate the inventive arrangement, in which the driver 7 is generally in the form of a cylindrical sleeve which is totally enclosed externally by the outer tube 10, so that in this case said tube will reach all the way to the bit head 13. The driver 7 is thus fully protected from the external affect of drill cuttings flowing back along the outside of the bit head and the outer tube. This allows the driver to be made of a much softer material than the material from which the drill bit 1 and its shaft 3 is made.

The driver will suitably be made of a material based on an alloy other than iron. The alloy will conveniently have a frictional coefficient of ≦0.25 in respect of a nonlubricated surface against steel, and a coefficient of thermal conductivity of ≧320 W/m°K. Examples of alloys that fulfil these requirements are alloys of bronze and copper.

As mentioned before, the outer tube 10 is preferably made of steel and may be provided with a harder outer coating to further reduce abrasive wear by the drill cuttings. 

1. An arrangement pertaining to down-the-hole hammers in which a driver (7) is adapted to transfer torsion forces between a rotating outer tube (10) and a drill bit (1) of the hammer, characterised in that the outer tube (10) is made of steel and is arranged outwardly surrounding all of the driver (7), and that the driver is made of a softer material than that in the outer tube (10).
 2. An arrangement according to claim 1, characterised in that the driver (7) is made of a bronze alloy.
 3. An arrangement according to claim 2, characterised in that the driver (7) is made of a copper alloy.
 4. An arrangement according to claim 3, characterised in that the outer tube (10) has an outer coating that consists of a material which is harder than the material from which said tube (10) is chiefly comprised. 